Field of the Invention
The present invention relates to carbon molecular sieve membranes and gas separations utilizing the same.
Related Art
Membranes are viewed as selective barriers between two phases. Due to the random thermal fluctuations within the polymer matrix, gas molecules from the high partial pressure side sorb into the membrane and diffuse through under the influence of a chemical potential gradient, and finally desorb to the low partial pressure side. Two terms, “permeability” and “selectivity”, are used to describe the most important properties of membranes-productivity and separation efficiency respectively. Permeability (P) equals the pressure and thickness normalized flux, as shown in the following equation:
                              P          i                =                                            n              i                        ·            I                                Δ            ⁢                                                  ⁢                          p              i                                                          (        1        )            where ni is the penetrant flux through the membrane of thickness (l) under a partial pressure (Δpi). The most frequently used unit for permeability, Barrer, is defined as below:
                    Barrer        =                              10                          -              10                                ⁢                                                    cc                ⁡                                  (                  STP                  )                                            ·              cm                                                      cm                2                            ⁣                              ·                s                ·                cmHg                                                                        (        2        )            Selectivity is a measure of the ability of one gas to flow through the membrane over that of another gas. When the downstream pressure is negligible, the ideal selectivity (based upon the permeabilitles of pure gases) of the membrane, can be used to approximate the real selectivity (based upon the permeabilities of the gases in a gas mixture). In this case, the selectivity (αA/B) is the permeability of a first gas A divided by the permeability of a second gas B.
Currently, polymeric membranes are well studied and widely available for gaseous separations due to easy processability and low cost. In particular, polyimides have high glass transition temperatures, are easy to process, and have one of the highest separation performance properties among other polymeric membranes. The patent literature (including US 2011/138852; U.S. Pat. No. 5,618,334; U.S. Pat. No. 5,928,410; and U.S. Pat. No. 4,981,497) discloses one particular class of polyimides for use in polymeric gas separation membranes that is based upon the reaction of a diamine(s) with 2,2-bis(3,4-dicarboxyphenyl) hexafluoropropane dianhydride (6FDA).
The selectivities of carbon molecular sieve (CMS) membranes, however, have been shown to have attractive separation performance properties exceeding those of polymeric membranes.
CMS membranes are typically produced through thermal pyrolysis of polymer precursors. For example, it is known that defect-free hollow fiber CMS membranes can be produced by pyrolyzing cellulose hollow fibers (J. E. Koresh and A. Soffer, Molecular sieve permselective membrane. Part I. Presentation of a new device for gas mixture separation. Separation Science and Technology, 18, 8 (1983)). In addition, many other polymers have been used to produce CMS membranes in fiber and dense film form, among which polyimides have been favored.
CMS membranes have also been produced from a wide variety of 6FDA-based polyimide precursors including the following specific examples.
Shao, et al. disclosed that gas separation performance of CMS membranes (films) pyrolyzed from different morphological precursors is strongly dependent on pyrolysis temperature (Shao, et al., Journal of Membrane Science 244 (2004) 77-87). The tested CMS membranes included those based upon 6FDA/PMDA-TMMDA and 6FDA-TMMDA, where PMDA is pyromellitic dianhydride, and TMMDA is tetramethylmethylenedianiline.
Low, et al. disclosed CMS membranes (films) pyrolized from pseudo-Interpenetrating networks formed from 6FDA-TMPDA polyimide and azide, where TMPDA is 2,3,5,6-Tetramethyl-1,4-phenylenediamine (Low, et al., Carbon molecular sieve membranes derived from pseudo-interpenetrating polymer networks for gas separation and carbon capture, Carbon 49 (2011) 2104-2112).
Swaidan, at al. disclosed the study of CH4/CO2 separations using thermally rearranged membranes and CMS membranes (films) pyrolized from polyimides based upon 6FDA and 3,3,3′,3′-tetramethyl-1,1′-spirobisindane-5,5′-diamino-6,6′-diol (Swaidan, et al., available online, accepted for publication on Jul. 28, 2013).
Kiyono, et al. disclosed the effect of pyrolysis atmosphere upon the performance of CMS membranes (films) pyrolyzed from 6FDA/BPDA-DAM, where DAM is 2,4,6-trimethyl-1,3-phenylene diamine and BPDA is 3,3,4,4-biphenyl tetracarboxylic dianhydride (Kiyono, et al., Effect of pyrolysis atmosphere on separation performance of carbon molecular sieve membranes, Journal of Membrane Science 359 (2010) 2-10).
Xu, at al. disclosed CMS membranes (hollow fibers) pyrolyzed from polyimides based upon BTDA-DAPI (Matrimid® 5218), 6FDA-DAM, and 6FDA/BPDA-DAM, where BTDA is 3,3′,4,4′-benzophenone tetracarboxylic dianhydride, DAPI is diaminophenylindane, DAM is 2,4,6-trimethyl-1,3-phenylene diamine. and BPDA is 3,3,4,4-biphenyl tetracarboxylic dianhydride (Xu, et al., Olefins-selective asymmetric carbon molecular sieve hollow fiber membranes for hybrid membrane-distillation processes for olefin/paraffin separations, Journal of Membrane Science 423-424 (2012) 314-323).
Fuertes, et al. disclosed the preparation and characterization of CMS membranes (films) pyrolyzed from Matrimid® and Kapton®, where Kapton® is a polyimide based upon pyromellitic dianhydride and 4,4′-oxydiphenylamine (Fuertes, et al., Carbon composite membranes from Matrimid® and Kapton® polyimides for gas separation, Microporous and Mesoporous Materials 33 (1999) 115-125).
Tin, et al. studied the permeation of CO2 and CH4 with CMS membranes (films) pyrolyzed from P84 polyimide based BTDA-TDI/MDI, where tetracarboxylic dianhydride and MDI is 80% methylphenylene-diamine+20% methylene diamine (Tin, et al., Separation of CO2/CH4 through carbon molecular sieve membranes derived from P84 polyimide, Carbon 42 (2004) 3123-3131).
Park, et al. studied the effect of different numbers of methyl substituent groups on block copolymides (PI-X) used to formulate CMS membranes (films). The block copolymides included those based upon BTDA-ODA/m-PDA, BTDA-ODA/2,4-DAT, and BTDA-ODA/m-TMPD, where ODA is 4,4-oxydianilne, m-PDA is 1,3-Phenylenediamine and 2,4-DAT is 2,4-diaminotoluene (Park, et al., Relationship between chemical structure of aromatic polyimides and gas permeation properties of their carbon molecular sieve membranes, Journal of Membrane Science 229 (2004) 117-127).
Hosseini, et al. compared the performance of CMS membranes pyrolyzed from each of Torlon (a polyamide-imide), P84, or Matrimid alone, and also in binary blends with polybenzimidazole (PIB), where Torlon (Hosseini, et al., Carbon membranes from blends of PBI and polyimides for N2/CH4 and CO2/CH4 separation and hydrogen purification, Journal of Membrane Science 328 (2009) 174-185).
Yoshino, et al. disclosed the separation of olefins/paraffins using a CMS membrane (hollow fiber) pyrolyzed from a polyimide based upon 6FDA/BPDA-DDBT, where DDBT is 3,7-diamino-2,8(6)-dimethyldibenzothiophene sulfone (Yoshino, et al., Olefin/paraffin separation performance of carbonized membranes derived from an asymmetric hollow fiber membrane of 6FDA/BPDA-DDBT copolyimide, Journal of Membrane Science 215 (2003) 169-183).